Tasmanunitary authority, northwestern South Island, central New Zealand. It is bounded by Tasman and Golden bays and Nelson city on the northeast. Administratively, it is bordered by Marlborough unitary authority and Canterbury local government region regional council on the east and by West Coast local government region regional council on the south and west. The authority is drained by the Buller, Motueka, and Aorere rivers and their tributaries. Rotoroa is the largest lake. Most of the authority is more than 3,000 feet (900 metres) in elevation and largely inaccessible, since it is dissected by the Tasman, Wakamarama, Peel, and Arthur mountain ranges.

In 1642 the Dutch navigator Abel Tasman anchored west of Separation Point in Golden Bay. His encounter there with the Maori was a tragic one, and Tasman sailed away naming the area Murderers’ Bay. In 1770 Captain Capt. James Cook sailed past Golden Bay beyond Separation Point into Tasman Bay; the latter appeared landlocked, and Cook named it Blind Bay. In 1772–73 Cook returned to Blind Bay and renamed it Tasman Bay, mistaking it for Tasman’s Murderers’ Bay. In 1827 J.-S.-C. Dumont d’Urville reached Tasman Bay; from that time the nucleus of European settlement was the lowlands south of Tasman Bay. The authority’s early development included small-scale farming and timber milling with sporadic coal mining. Gold was found in Buller Gorge in 1859.

Subsequently the mining of asbestos, clay, limestone, and coal became important in the locality. Intensive cultivation of tobacco, fruits, and vegetables is carried on in the valleys and lowland areas. The authority’s industries are predominantly rural in nature and include food processing and packaging, manufacture of pulp and paper, sawmilling, and vehicle repair.

The valleys and lowlands in the north contain most of the authority’s population, with the major towns being Motueka, Richmond, Wakefield, Riwaka, and Collingwood. Abel Tasman and Nelson Lakes national parks are recreational resources in the region. The only major road traverses the Buller River valley (east to west), connecting Westport (west) with Nelson city and Motueka (east). Area 3,773 square miles (9,771 square km). Pop. (2003 est.2006) 4148,352306.